We want to have different window types for different displays, so we can
write code like this:
#if GDK_WINDOWING_X11
if (GDK_IS_X11_WINDOW (window))
{
/* do x11 stuff */
}
else
#endif
#if GDK_WINDOWING_WAYLAND
if (GDK_IS_WAYLAND_WINDOW (window))
{
/* do wayland stuff */
}
else
#endif
{
/* do stuff for unsupported system */
}
This requires different GdkWindow types and we currently don't have
that, as only the GdkWindowImpl differs. With this method, every backend
defines a custom type that's just a simple subclass of GdkWindow. This
way GdkWindow behaves like all the other types (visuals, screens,
displays) and we can write code like the above.
Move everything dealing with compound text to be X11 specific
Only gdk_text_property_to_utf8_list and gdk_utf8_to_string_target
are kept across backends, so add vfuncs for these.
Also, remove the non-multihead-safe variants of all these.
